Dear R-list,
I have a statistical problem with the comparison of short time-series,
representing densities of fish in different streams. For each stream (6 in
total, here below showed only part of the dataset) I have 8 years of density
data, as follows:
year density stream
1 2000 0.51 stream1
2 2001 0.87 stream1
3 2002 0.68 stream1
4 2003 0.56 stream1
5 2004 0.50 stream1
6 2005 0.51 stream1
7 2006 1.07 stream1
8 2007 1.02 stream1
9 2000 0.23 stream2
10 2001 0.43 stream2
11 2002 0.56 stream2
12 2003 0.59 stream2
13 2004 0.52 stream2
14 2005 0.36 stream2
15 2006 0.28 stream2
16 2007 0.38 stream2
17 2000 0.07 stream3
18 2001 0.06 stream3
.
.
There is a clear problem of non-indipendence of data, so this seem to
preclude a classical ANOVA and subsequent pairwise comparisons. What I would
like to test is: are mean densities different among streams from 2000 to
2007? Is it sufficient and appropriate a test of correlation (using rcorr of
the library Design, for example) to test if density trends in time are
similar among streams?
Any help would be greatly appreciated.
Simone
Simone Vincenzi, PhD
Department of Environmental Sciences
University of Parma
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